Relict Glacial Lakebed Ecosystem wetlands are the most common and extensive on the Kenai Lowlands project area. Large ice-dammed lakes covered a substantial portion of the Lowlands during Wisconsin time.  Fine-grained sediments were left behind after the lake drained.  These fine-grained sediments drain poorly, so perch a water table.  A perched water table combined with a high latitude maritime climate supports peat development.  Peat has built up into the patterned fens which now occupy the vast ancient lake bottoms.  Patterned peatlands such as these are well-documented (Sjors, 1963; Moore and Bellamy, 1974; Glaser, et. al., 1981; Vitt, 1994) and are described using many names (e.g. patterned fen, ribbed fen, strangmoor, apamoor). 

Ideally expressed, patterned fens consist of tree islands in a matrix of interconnecting ridges (strangs) and intervening flarks (low spots occupied by sedge communities) and open water pools.  The strangs are more or less linear topographic high spots.  On the Kenai Lowlands they are on the order of about 0.5 to 1.5 meters high and between about 50 and 100 m long.  The intervening flarks and pools are typically about 50 cm to 1.5 m deep and between 5 and 20 m wide by about 10 to 50 m long.  This complex of strangs, flarks and pools is oriented perpendicular to groundwater flow.  Tree islands are approximately circular in the matrix of strangs, flarks and pools.  Often, only weakly expressed strangs and flarks are present.

This pattern  is especially well developed in the large fen northwest of the Kenai Airport, shown in the aerial photograph at the top of this page, on the right.  The pattern is subdued at many other locations, but it probably represents the dominant peatland process on the lowlands.  South of Clam Gulch, lakebeds are frequently smaller and occupied by deeper, more uniform peat, and the strang-flark tree island complex is only subtly represented, or present in a small area of a larger peatland.

The pattern is probably produced by a convergence of multiple processes (Moore and Bellamy, 1974) depending on slope, substrate and regional climate.  Processes that initiate this pattern may be autogenic or allogenic (independent of peat accumulation processes).  An example of an allogenic process is slippage of peat along a bedrock slope (Pearsall, 1966).  The autogenic process is the differential accumulation of peat in micro-sites (Foster, et. al., 1988) and is self-maintaining, once established. 

Researchers have found support for self-maintaining autogenic processes in mires of  Sweden, Quebec and western Labrador, where the water table is stable throughout the year, (Foster and Fritz,1987; Foster, et. al., 1988).  Secondary lower, wetter areas form on the peat surface, once a peatland becomes established on a site.  These lower areas are unrelated to the micro-relief of the underlying mineral surface.  The low areas are self-perpetuating, because slower peat accumulates more slowly in wetter spots.  Conversely, strangs build up in drier areas where peat accumulation is more rapid.  Overall, the surface on those fens has become wetter.  Flarks have become pools, and pools have coalesced. 

However, pools can drain and dry out, allowing flark and lower strang vegetation to invade (Foster and Fritz,1987).  The large fen east of Anchor Point contains two large drainage systems.  That fen may have been similar to the one northwest of the Kenai airport before the two systems drained most of the pools (aerial photo on the left, above).  The fen northwest of Kenai seems to be drying, probably due to ditches associated with the airport, groundwater withdrawal, and climate change.

Foster et. al. (1988) note that in areas of drier climate, or seasonal drought, peat accumulation between flarks and strangs equalizes, and patterns can become subdued.  Peat accumulation can be quite variable, both spatially and temporally (Waddington and Roulet, 2000).  Kenai fens are different than those studied in Quebec, Labrador and Sweden as our climate is drier, and probably more inter- and intra-annually variable.  Early summer pools dry to flarks by July during dry years on the Kenai.  Strang vegetation may invade Kenai flarks during periods of drought; and flarks may become pools during wet times.   

Apparently stable sphagnum islands are found in the centers of many pools on the Kenai.  This contrasts with the degrading peat found at fen edges in Quebec, Labrador and Sweden.  The degrading peat there is due to expanding pools.  The stable, and perhaps expanding sphagnum islands here might indicate contracting pools.  Kenai sphagnum islands could be feeding on groundwater discharge.

Patterned fens can have deep peat layers.  On the Kenai Lowlands, the peat is typically around 1.3-2 meters (about 4-6 feet) thick, but can be much thicker.  Soils are largely hemic (partly decomposed) Histosols, mainly of the Starichikof soil series.  Where peat is a little thinner, Doroshin soils dominate (with less than 130 cm of organic material), and often a complex with Starichkof soils in the center, and Doroshin soils at the margin of the peatland is present.  Fibric Salamatof soils occur occasionally.

Salamatof soils were mapped extensively during the soil survey published in 1971.  These un-decomposed histosols may have actually been more prevalent then, indicating a climate more conducive to bog formation.  However, access was limited then, and they may have been mapped in error.

NWI and HGM

These fens are palustrine wetlands in the US Fish and Wildlife Service's National Wetlands Inventory (NWI) classification, with a variety of plant dominants from herbaceous emergents (PEM) to shrubs (PSS) and forest (PFO), with hydrologic regimes ranging from saturated through permanently, semi-permanently, and seasonally flooded (PSSB, PEMH, PEMF and PEMC, respectively). 

In an HGM classification system (Tiner, 2003) most fit loosely into the Terrene Flat/Slope groundwater-dominated throughflow category.  They may have once been created by paludification, but that process is no longer active in most lowland peatlands.  Many form the headwaters to small streams, particularly short-run streams near the coast.  Delineating the headwater portion of the large peatland might be impossible.

Plant relationships

Groups of plants tend to occur at the same positions along the gradient from pool or flark to strang summit.  If a particular site has a long enough gradient, these plant communities sometimes resolve into monospecific (single species) stands.  Using repeated observations, an idealized cross section can be constructed of which plants occur where on the gradient from pool to strang summit.  Knowing where plants occur on this idealized gradient enables interpretation of the landscape at sites where the gradients are fuzzier.

 Introduction and Key to Plant Communities  

Introduction and Key to Ecosystems

    Kenai Hydric Soils    Map Unit Summary    Methods    Glossary

03 May 2007 18:04